The present invention relates to a method of increasing the adhesion between silica and gold. The method comprises joining the silica and gold followed by annealing in an oxidizing atmosphere.
It is well known that gold does not adhere well to ceramics such as silica. The reason for this lack of adhesion is the differences in bonding exhibited by these materials - i.e., silica adheres to substances by electrostatic bonds whereas gold adheres to substances by shared electron bonds. As such, a direct molecular bond between the materials is impossible.
It is often desirable in the electronics industry to use gold metallization and ceramic coatings on devices such as integrated circuits. However, because of the poor adhesion between these materials, delamination and circuit failure can occur.
Numerous approaches have been attempted to solve this problem. For instance, metallic oxides, metallic adhesion layers and adhesives have been applied between the ceramic and the gold to promote adhesion. These approaches, however, each have disadvantages such as cost, complexity, degree of adhesion, and electrical characteristics.
de Bruin et al. in U.S. Pat. No. 4,050,496, teach a simplified method of bonding comprising joining the ceramic and gold followed by heating in air. The reference teaches that the heating must be conducted at a temperature greater than about 800.degree. C. to allow the materials to chemically react. As is obvious, however, this process is disadvantageous in that the high temperature may damage the substrate. Moreover, the silica described therein was not derived from hydrogen silsesquioxane resin.
The present inventors have now discovered that silica derived from hydrogen silsesquioxane resin can be bonded to gold by low temperature annealing in an oxidizing environment.